The known bases are usually constituted by a substantially rectangular peripheral frame, which is provided with one or more bearing legs and carries in its interior a succession of transversal parallel rollers defining a bearing surface for cartons.
On the other hand, in many cases, there are provided special conveying units for advancing cartons with coplanar and parallel conveyor belts which are included in a suitable space inside the roller succession, in such a way as to allow the conveyor belts to engage the carton bottom. These units are usually supported laterally by suitable longitudinal section irons fixed to the frame, while the spaces between the irons and the longitudinal side members of the frame are filled with respective successions of transversal rollers of reduced length.
In the present machines of this type there exists the problem of replacing the conveyor belts when they are worn. At such time, in fact, it is necessary to detach the unit from the rest of the base, opening at this end the relative electric and pneumatic connections. Obviously, this requires considerable time, that reflects on the machine's productivity and consequently on the production costs.